I can’t remember any instances of animal physiology being mentioned, but her parents do call her “kitten” at times! It’s not unthinkable that human parents would use that term endearingly, but it’s still pretty weird.

According to the devs, the original plan was that the species would be stand-ins for races but they opted to make them canonically human with animal representations instead, and opted to go for visual distinctiveness instead. (Although arguably the various species are still racial stand-ins, at least judging by the concordances with name etymologies; for example, all of the cats have Polish names.)

There’s a couple of minor holdovers from the original idea, such as the ball of yarn in the “clue box,” which they wanted to get rid of but it was just so darn much FUN.

But anyway Word Of God is that the characters are human, we just see them through cartoon animal eyes.